The most well-known type of pluripotent stem cell is the embryonic stem (ES) cell. However, the generation of embryonic stem cells can only be derived from embryos, and it has so far not been feasible to create patient-matched embryonic stem cell lines. Induced pluripotent stem (iPS) cells are a type of pluripotent stem cell that can be generated directly from somatic (differentiated) cells. Since iPS cells can be derived directly from adult tissues, they not only bypass the need for embryos, but can be made in a patient-matched manner, which means that each individual could have their own pluripotent stem cell line. iPS cells may be generated through the ectopic expression of Oct 4, Sox2, Lkf4, and c-Myc (OSKM) transcription factors in somatic cells, leading to global epigenetic changes during reprogramming. Chromatin regulatory proteins mediate epigenetic remodeling during iPS cell formation, and loss-of-function studies have shown that Polycomb proteins are potent regulators of cell fate reprogramming. However, iPS cells may retain epigenetic signatures of their somatic cell of origin that can persist through extended passaging, and the molecular mechanisms responsible for epigenetic memory are unclear.
In ES cells, long noncoding RNAs (lncRNAs) associate with chromatin regulators such as Polycomb proteins and are required to repress lineage-specific genes in the pluripotent state. LncRNAs have been shown to target chromatin regulatory complexes throughout the genome in various developmental settings, but relatively little is known about lncRNAs in the context of cellular reprogramming.